[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: dynamic vs. static typing



You wrote in article <n0alvp4j.fsf@ccs.neu.edu> in gmane.comp.lang.lightweight:
> The reason there are no `TRULY heterogeneous lists' is because it is
> always possible to create a discriminated union type that covers all
> elements.
> 
> It is especially pointless if you fold all operations on objects
> into the object interface itself.
> 
> But if you take the view that certain operations (like intensional
> equivalence or intensional identity) are independent of the objects,
> then the notion of heterogeneous lists becomes much more interesting.
> Permutation, for example, becomes possible.

You seem to be claiming that permutation of a truly heterogeneous list
is impossible without taking the view that certain operations (like
intensional equivalence or intensional identity) are independent of the
objects.  I probably misunderstood you, but I don't see how this claim
is true, if you are in fact making it.  Permutation of lists can be done
for a homogeneous list without knowing what type all of the objects in
the list are (the type of such a permutation function looks like "forall
a. [a]->[a]"); as a special case, one can permute a list whose element
type is homogeneously "I have no idea" (substitute "exists b. b" for
"a").

-- 
Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig
Sexy types in action: http://www.eecs.harvard.edu/~ccshan/cs252/usage.pdf
new journal Physical Biology: http://sansom.biop.ox.ac.uk/images/physbio.gif
What if All Chemists Went on Strike? (science fiction):
http://www.iupac.org/publications/ci/2003/2506/iw3_letters.html

Attachment: signature.asc
Description: Digital signature